photoresponse

Photoresponse is the response of a material, device, or organism to light. In physics and engineering it describes how incident photons generate an electrical or optical signal in a photodetector or solar cell. In biology, it refers to the cellular and biochemical cascades triggered by light, such as phototransduction in retinal cells or the light-regulated development of plants.

In photodetectors, photoresponse is quantified by metrics such as responsivity (output per unit optical input), quantum efficiency, spectral response, noise, dark current, dynamic range, and speed. Responsivity is usually expressed in amperes per watt or volts per watt; quantum efficiency is the fraction of absorbed photons that produce charge carriers. The spectral response shows how sensitivity varies with wavelength. Speed is described by rise and fall times or bandwidth. Real devices may exhibit nonlinearity, saturation, and various noise sources. Common devices include photodiodes, photoconductors, phototransistors, CCD/CMOS imagers, photomultiplier tubes, and solar cells, using materials such as silicon, III–V semiconductors, perovskites, or two-dimensional materials.

In biology, the photoresponse encompasses phototransduction in sensory cells of animals, where light triggers a biochemical cascade that converts photons into neural signals. In plants, photoreceptors such as phytochromes, cryptochromes, and phototropins detect light to regulate growth, development, and circadian rhythms.

Applications range from imaging, spectroscopy, and optical communications to solar energy and environmental sensing. The study of photoresponse integrates material science and biology to develop faster, more sensitive, and spectrally tunable light sensors and light-driven biological insights.